In the year 2104, the Solar Union (the government of Earth and the solar system) faces trouble from three former colonies. Under the guise of negotiations, the colonies' forces attack and capture three mining worlds: Neptune's moon Triton, the Earth-like planet Romulous and the water world Pacifica. Earth's survival is at stake. It is the player's mission to strike back at the invaders and recapture the three worlds. Earth's full arsenal of ground, air and naval forces is standing by.
This version of Nectaris is an updated and expanded version of the original game with a new background story, an entirely different graphical style and lots of new content. It includes all maps (the setting of which has been changed from the Earth's moon to Triton) and units from the original game. Two new sets of maps (the Romulous and Pacifica campaigns) have been added for a total of 96 levels. There are also many new units, more than doubling the number of the original. The non-lunar settings of the new campaigns allow for naval units for the first time (including submarines and ship-based aircraft), as well as such units as helicopters, jump-jet infantry and paratroopers.
Gameplay is unchanged from the original. Units move and attack in turns on a tactical map. Each unit has different ratings for attack and defense as well as range. Combat is decided by various factors including the combatants' abilities, troop strength and experience, terrain, and the positioning of support units.
Units cannot be created. The only way to gain new units is to capture depots containing neutral units.
To win each map, either the enemy's headquarters must be captured or all his forces be destroyed.
At any time between battles, the campaign can be switched among the three different worlds. The last mission beat on each world is automatically saved, and earlier maps can be accessed through passwords. It is also possible to save the game during a battle.
In addition to the single player maps, there are also 8 special multiplayer maps, which can be played by up to four players (or AIs, if not enough people are available). In multi-player mode, various diplomatic relations can be set between the different parties, from alliances to all-out war.